1. Field of the Invention
The present invention relates to an air conditioner for a vehicle.
2. Description of the Related Art
An air conditioner for a vehicle has characteristics in which a ventilation resistance in an air conditioning casing connected to a fan (air blowing unit) varies in accordance with operation states such as a blowing mode and an air conditioning preset temperature.
Concretely, in a comparison between face mode in which air is mainly blown to the upper body of a passenger and foot mode in which air is mainly blown to the lower body of a passenger, the ventilation resistance of the face mode is usually smaller than that of the foot mode.
In an automatically controlled air conditioner for a vehicle, the blowing mode is determined based on the air conditioning preset temperature or the like. Therefore, the blowing mode varies as the air conditioning preset temperature varies and, then, the ventilation resistance varies.
As shown in FIG. 4, the fan is actuated at an intersection between a graph showing air blowing property of a fan and a graph showing a ventilation resistance, and the noise of the fan is minimized at a point of actuation at which the maximum efficiency can be obtained.
The maximum air volume is needed in a rapid cooling operation, in which an air conditioning load is maximized, in summer. Therefore, in a usual air conditioner for a vehicle, the air blowing property of the fan is optimized in accordance with a ventilation resistance in face mode which is heavily used for cooling in summer and, thus, the noise and energy consumption of the fan can be reduced.
Therefore, in foot mode whose ventilation resistance is largely different from that of face mode, the fan has to be operated at a point of actuation deviated from the point of actuation in which the maximum efficiency can be obtained and, thus, the noise is increased and air blowing efficiency is reduced.
In a heating operation, the blowing mode is usually switched to foot mode, and a heated air is blown to a vehicle compartment. However, when a heating load is large in winter, air having a low temperature has to be drawn and heated and, thus, it is difficult to increase the temperature of the air, blown to a vehicle compartment, to a predetermined temperature in a short time.